Cool core hot cavity spark plug



1955 G. F. WRIGHT ET AL 2,702,537

COOL CORE HOT CAVITY SPARK PLUG Filed Aug. 14, 1951 2 Sheets-Sheet l I 3: 5- v V 4? IN V EN TOR. wager we/m/r BY GA K4050 w. MFWTOA/ A wow/5V5 F b.22,195s G. F. WRIGHT Em 2,102,531

COOL CORE HOT CAVITY SPARK PLUG Filed Aug. 14, 1951 2 Sheets-Sheet .16

I 1 J F 65 r I 644 44 50 i I 4:2 7 I 47 IN VEN TOR. G/LBE ET F WE/Ghr .BY GAKZOED VV- NEWTON A TTOEWE Y5 coo com: nor CAVITY SPARK PLUG Gilbert F. Wright, Renton, and Gaylord W. Newton, eattle, Wash, assignors to Boeing Airplane Company, Seattle, Wash, a corporation of Delaware Appiication August 14, 1951, Serial No. 241,812

13 Claims. (Cl. 123-469) This invention concerns a spark plug including an insulating core construction which is cooler than ordinarily is the case, and a cavity 'wall encircling the core which is hotter than usual, and is particularly advantageous for use in antechamber type spark plugs.

Various attempts have been made in the past to design a suitable spark ping incorporating anantechamber on the theory that combustible mixture admitted to such antechanrber would be ignited to project a tongue of flame into the combustion chamber of an engine cylinder, and thereby increase the efficiency of combustion. Unfortunately most of these designs have not increased the eifectiveness of combustion, but have caused preignition and excessive fouling. The present invention was evolved after a series of experiments had been conducted in an attempt to discover the difiiculty with these previous designs.

The principal object of the present invention is to provide a spark plug which will not cause preignition of the combustible mixture in an engine cylinder or other combustion space, but which, on the contrary, will increase the efficiency of combustion and improve the power produced by t he combustion.

A further important object is to construct a spark plug, particularly of the antechamber type, so that it will have long operating life without fouling, even though used with gasoline containing lead compounds or other antidetonants, and which will efliectively fire a leanrnixture.

Still another object is to utilize the principles of this invention in spark plugs for ditferent specific applications, such as for airplane reciprocating piston engines, for automobile engines and 'for outboard motorboat enmes.

g it has been found that a spark plug of the type embodying the present invention will be substantially free from fouling by carbon or lead compounds even after it has been operated for a long time under conditions which ordinarily are most likely to result in such fouling, such as where the engine is run alternately at high speed and low speed. An outboard marine motor, for example, is frequently subjected to operation of this type during fishing, in which use the motor will first be operated at high speed to propel the boat to a desired location for fishing, then the engine will' be idled down to trolling speed, and if the fishing is not successful at the particular location first tried, the engine again will be operated at high speed to propel the boat to a different location for fishing where the engine again will be operated at low speed during trolling. Such high and low speed alternate operation of an outboard marine motor may occur at varying intervals over a period of several hours. This type of operation will cause the conventional outboard engine spark plug to become so fouled, as to be inoperative within a period of a few hours, even though so-called white gasoline is used in the engine, namely gasoline which does not contain any tetraethyl lead. When a spark plug incorporating the present invention is used, however, it will remain in satisfactory operating condition after being used for more than one hundred hours in an outboard engine powered with gasoline containing tetracthyi lead or other lead compounds.

The remarkable antifouiing characteristics of the present spark plug is the principal advantage of the present invention over the spark plug disclosed in the application of Gilbert P. Wright, Serial No. 163,155, filed May 2'5, 1950, now Patent No. 2,642,054, issued June 16,

ited States Patent 2,702,537 Patented Feb. 22, 1955 1953. As in that application, thedesignation spark plug mechanism is used in this specification to embrace both an arrangement in which the antechamber is formed in an adaptor to be screwed into the engine and into which a standard spark plug is then screwed, and also a spark plug which is itself specially constructed in accordance with the invention, although the latter type of device is preferred.

'It has been found that particularly in an antechamber type of spark plug of the types previously proposed preignition has been a serious problem, resulting in loss of engine power, because of the excessive heating of some element of the spark plug, usually the tip of the insulating core and its central electrode, and the construction of the present invention has for a principal purpose to accomplish the dissipation of heat'from these'elements. The problem of preventing fouling by deposit of carbon and lead compounds from the fuel has also been very troublesome, and a companion object is to increase the temperature of the cavity wall encircling the core tip to reduce such deposits. Design of this cavity for fouling without decreasing lean mixture firing ability is made possible by locating the spark gap in the antechamher outside of this cavity.

The spark plug mechanism does not have any special heat radiating structure, and consequently the mass of the engine itself, which is either air-cooled or liqnid-cooled, is relied upon for absorption or dissipation of the heat from the spark plug. The problem is to conduct the heat readily from the core and central electrode to the engine. This result is accomplished by two expedients in the present invention, first, by impeding the transfer of heat from the less highly heated parts of the spark plug mechanism, and specifically from a thimble or bushing encircling the central electrode and inner end of the insulating core carrying it, and which thimble or bushing carries the electrode or electrodes cooperating with the central electrode, and second, by facilitating transfer of heat from the central electrode and insulating core to the engine by increasing the conductive ability of the path which such heat must traverse. More specifically, contact between such thimble or bushing and the body of the spark plug mechanism is reduced to decrease the path or paths through which heat may travel to theengine and to incorporate between the core and body of the spark plug rechanism metal having high heat conductivity to' gxlciiedite transfer of heat from the core to the spark plug o y.

Advantages of the specific types of representative constructions shown in the accompanying drawings to accomplish the objects of this invention are discussed in the following particular description of the invention.

Figure 1 is a longitudinal sectional view through the center of a spark plug of aircraft type, incorporating the invention. Figure 2 is a longitudinal sectional view through the center of the spark plug body showing a side view of the core of a different type of aircraft spark plug embodying the invention.

Figure 3 is a longitudinal sectional view through the center of the casing of an automobile type spark plug incorporating the invention, with the core in side elevation.

Figure 4 is a longitudinal sectional view through the body of a spark plug incorporating the invention, and particularly adapted for use in outboard engines, a side view of the core being shown; and Figure 5 is a similar view of the same general type of spark plug but of different size.

Figure 6 is a side elevation view of an automotive spark plug similar to that of Figure 3, the core being shown in elevation, but which spark plug has no antechamber.

in spark plugs of the conventional type which do not have an antechamber the electrodes themselves ordinarily project into the combustion space of the engine, as would those of the spark plug shown in Figure 6. The end of the spark plug body beyond which these electrodes project is then threaded to be screwed into a port in the engine, so that the portion of the body, the inner surface of which is engaged by the spark plug core, is in direct conductive heat transfer relation to the engine by the threaded engagement therewith of the outer surface of this portion of the spark plug body. Consequently a rather direct path is provided for dissipation of heat from both electrodes to the engine through the body, though that from the core would be longer.

In spark plug mechanisms in which it has been proposed heretofore to incorporate an antechamber, whether that antechamber is formed in an adaptor into which the spark plug is screwed as in the Sobel Patent No. 2,361,975, or is formed in the body of the spark plug as is that disclosed in Baldwin et al. Patent No. 1,671,268, for example, the threaded portion of the spark plug body or adaptor to be screwed into the engine has been at the inner end of the spark plug mechanism, spaced a substantial distance inwardly from the grounded electrode or electrodes. The hot gas heats the electrodes and their supporting elements, and Where no special heat radiating structure is provided on the spark plug mechanism itself, the only way in which such heat can be dissipated is by conduction through the body of the spark plug mechanism to the engine.

In spark plug mechanisms incorporating antechambers of types previously proposed, such as in the examples given, heat from the electrodes and their supporting structures could be conducted to the engine only by its travel longitudinally of the spark plug mechanism body from the mounting structure for both electrodes. In these constructions the grounded electrode mounting structure is interposed between the core in which the central electrode is mounted and the engine to which the heat must be transferred. Transference of heat from one part to another necessarily requires a temperature difierential of such parts. Heating that portion of the body adjacent to the grounded electrode, which body portion is interposed between the engine mounted portion of the spark plug mechanism body and the core supporting portion of the spark plug mechanism body, creates a virtual block against transfer of heat from the core to the engine longitudinally through the spark plug body because of the small differential in temperature between the core and the portion of the body adjacent to the grounded electrode. The result of this situation is that the central electrode temperature will increase until heat will be conducted from the core through that portion of the spark plug mechanism body adjacent to the grounded electrode and thence to the engine. Consequently, the central electrode temperature is very substantially higher than the grounded electrode temperature.

Preignition of combustible mixture in a combustion chamber is caused by some portion of the engine or spark plug mechanism becoming excessively hot. If the central electrode of a spark plug is heated to an exceptionally high temperature for the reasons discussed, it will cause such preignition conditions. The purpose of the present structure, therefore, is to deter the transfer of heat from the grounded electrode or electrodes and supporting structure therefor to the adjacent portion of the spark plug mechanism body, and to facilitate the transfer of heat from the central electrode and core to such body and through it to the engine. By using these expedients the temperature differential between the central and grounded electrodes and their supporting structures is substantially reduced, the temperature of the grounded electrode or electrodes being higher than it would be otherwise, and the temperature of the central electrode and core being appreciably lower than otherwise it would be. Since it is the component at the highest temperature which causes preignition, the increase in temperature of the grounded electrode to equal that of the central electrode would not be detrimental, while the reduction in temperature of the central electrode thus achieved is extremely beneficial in preventing preignition, which enables the engine to produce more power.

Moreover, fouling of a spark plug by deposit of carbon and lead compounds around the core of a spark plug through which electricity may leak from the central electrode to the spark plug body is reduced by the higher temperature of the wall of the cavity. For this reason also the present construction is advantageous, because particularly in an aircraft spark plug and in an outboard spark plug, efficient operation over extended periods is very desirable. Moreover, the cavity between the insulating core and the adjacent encircling wall may be designed for minimum fouling in the present plug without which encircles the antechamber 11. This antechamber has concave walls converging toward restricted neck 12 and flaring mouth 13 opening through the inner end of the spark plug. In the body cavity is received the bushing or thimble 2 carrying the grounded electrode 20. The inner end of this bushing seats on the internal body shoulder 14 at the larger end of the antechamber 11.

The thimble 2 is held in place by a ring 21, preferably of copper, which engages the outer end of the thimble and presses it axially against the body shoulder 14. Such body may have a further shoulder 15 adjacent to the inner end of ring 21, but preferably such ring does not press against shoulder 15 suificiently to prevent it from holding the thimble firmly against shoulder 14. The inner surface of the ring 21 is flared outwardly complementally to an inwardly tapered surface of the insulating core 3, preferably of ceramic material. This core is held in place in conventional fashion by the tube 16, the inner end of which is threaded externally to engage internal threads on the outer end of the spark plug body 1. Pressure may be exerted by the inner end of the sleeve against a shoulder 31) on the core by a yieldable ring 17, such as of copper, the core pressure swaging the soft ring 21 contiguously against the body and core.

In order to deter transfer of heat from the grounded electrode 20 to the portion of the spark plug body 1 immediately encircling it, the surfaces of the bushing in contact with the inner wall of the spark plug body are reduced. Such reduction is effected by forming annular grooves 22 in the bushing and making its diameter sl1ghtly less than the internal diameter of the spark plug body between shoulders 14 and 15. The bushing is then held firmly in place by contact of its inner end with the shoulder 14, but at the locations of grooves 22 has no contact with the spark plug body, and the annular ribs between such grooves act principally as centering elements to locate the grounded electrode 20 approximately and contact the inner wall of the spark plug body over a small arcuate portion of its periphery if at all. The bushing is therefore in poor heat transfer relationship to the spark plug body, so that instead of its adjacent portion being heated by heat conducted from the grounded electrode 20, such electrode and the bushing 2 would be heated to a higher temperature than would otherwise be the case if heat from the electrode supporting bushing could be transferred readily to the spark plug body.

On the contrary, the transfer of heat from the central electrode 31, which as shown is disposed to cooperate with the grounded electrode 20, is facilitated by providing in such electrode a core 32 of good heat conducting material such as copper. From this core heat may be conducted to the insulating core 3, thence to the ring 21 and the spark plug body 1. These parts will all be in good heat exchange relationship with each other because the central electrode core 32 will actually be pressed 1nt o contact with the ceramic core 3 which in turn is in intrmate contact with the ring 21, which should have a tight fit in the spark plug body.

While heat will be conducted quite rapidly from the central electrode 31 through its core 32, spark plug core 3, to the body 1 through the high heat conductrvlty copper ring 21 swaged into place between such core and body therefore, the transfer of heat from the grounded electrode 20 to such body through its supporting bushing 2 will be deterred, particularly by reason of the grooves 22. Consequently, the temperature of the body 1 ad acent to the grounded electrode supporting bushing Wlll be lower than it would be otherwise, enabling heat to flow from the core 3 lengthwise through the body to the threads 10, and into the engine. As a result the temperature of electrodes 20 and 31 will approach equalit and that of the central electrode will be kept low enough to prevent it causing preignition.

As in the spark plug of the Wright application Serial No. 163,155 mentioned previously, the inner end of bushing 2 still forms a shoulder in the antechamber 11, and the space between this bushing and the inner end of core 3 is small as compared to the volume of the ante chamber. The remainder of the spark plug core is rather conventional, including the conductive gas seal 33, the copper block 34, wire 35 interconnecting the copper block 34 and the copper electrode core 32, and the carbon cartridge 36 pressed against block 34 by the al -pars? spring 37. The terminal-38, screwed into the end of the core 3, may be engaged by the end of a wire received within the porcelain lined tube '16.

The spark plug shown in Figure 2 may have a core 3' of construction similar to a spark plug of Figure 1, except that the shape of its enlarged portion'diifers somewhat, and the copper ring 21 interposed between the core 3 and the spark plug body 1' is considerably thinner. The general shapes of the spark plug body and its antechamber 11 are the same, but the specific shape of the spark plug cavity inwardly of shoulder 14' differs somewhat from that of the spark plug in Figure 1.

In this form of spark plug the bushing or thimbie 2 is flatter than the bushing 2 of Figure 1, so that the space between the inner periphery of the Figure 2 bushing and core 3 extends transversely of the axis of the spark plug, instead of principally axially thereof as in Figure 1. Instead of the bushing having several spaced grooves in its periphery it has a single annular groove 22' defining annular ribs or flanges at opposite ends of the bushing which contact the spark plug body. The inner one of these flanges seats against the shoulder 14', while the outer one will fit loosely within the body cavity. in this instance there is no direct axial force applied to the bushing by the core 3 but such bushing is pressed into the body with a push fit prior to assembly of the core with the body. The flange 2', at least, will engage the body tightly.

It will be evident that the general effect of this spark plug construction is the same as that illustrated in Figure 1, namely that the groove 22' will impede the transfer of heat from the bushing 2 to the spark plug body, so that the temperature of the body adjacent to such ring will be lower than it otherwise would be. On the contrary, heat will be transferred more readily from the core to the body 1 through the copper ring 21', swaged into place between these two elements by screwing the tube 16 into the end of the body to press against the core. Again, therefore, the result will be that the temperature of the central electrode 31 is lower and the temperature of the grounded electrode is higher than would be the case otherwise.

In Figure 3 an automobile type of spark plug is shown, to which the principles of the present invention have been applied. in the body 4 is mounted the insulating core 5, so that the central electrode 50 is disposed longitudinally of the spark plug in the vicinity of the external body shoulder and the root end of the threaded portion 41. The grounded electrode 42 is carried by the bushing 43, the inner end of which engages the internal shoulder 44 of the spark plug body. This bushing is pressed to its seat by the core 5 pressing against the copper ring 51 tapered in cross section. Because the outer end of bushing 43 is rather wide so that it would have a substantial area of contact with ring 51, a heat insulating gasket 52 is interposed between the ring 51 and the bushing 43.

The spark plug of the type shown in Figure 3 would be factory assembled, during which operation pressure on the ceramic core 5 into the spark plug body would be effected in a suitable press, so as to swage the ring 51 as may be necessary to effect an intimate fit between the core 5 andthe spark plug body 4 and further to press the bushing 43 tightly against the internal body shoulder 44. In the same operation the securing ring 53 would be pressed firmly against the copper ring 54-, and while held in that position the outer end of the spark plug body would be rolled or otherwise bent inwardly to hold the ring 53 in core securing position.

In the spark plug of Figure 3 the bushing 43 has a flange 46 on its outer edge of a size to fit loosely in the internal bore of the spark plug body. In this spark plug structure, therefore, while the inner end of the bushing fits tightly against shoulder 44 to establish a good ground for the electrode 42, a relatively small area of contact between the bushing and the spark plug body is afforded through which heat can be conducted from the grounded electrode and its supporting bushing. Consequently that portion of the spark plug body adjacent to the bushing 43 would be at a considerably lower temperature because of the poor heat exchange relationship between the bushing and body. On the contrary, heat would be dissipated quite readily from the core 5 through the copper ring 51 to the spark plug body, through which it is transferred to the threadedportion 41 for conduction to: the engine. By use of this construction also, therefore, the central electrode can be maintained at a temperature little higher than the temperature of the electrode 42, so that the central electrode does not constitute an excessively hot element which would cause objectionable preignition. Also, because the space between bushing 43 and the inner end of the core 5 is small and the temperature of the bushing approaches that of the inner end of the porcelain core 5, there will be little tendency for carbon or lead compounds to be deposited in this space.

The outboard marine engine spark plugs shown in Figures 4 and 5 have proven to be remarkably free from fouling. The construction of these spark plugs is generally similar to that of the automobile spark plug shown inFigure 3. Moreover, the internal structure of the spark plugs shown in Figures 4 and 5 is identical and interchangeable, the only diiference being in the exterior dimensions of the body. In Figure 4 the body 6 is thinner than the body 6 in the spark plug of Figure 5, and the wall 6% of the antechamber 61 in the spark plug of Figure 4 is lighter than the corresponding wall 6% in the spark plug of Figure 5. Moreover, the length of the threaded portion 62 of the spark plug body in Figure 4 isshorter than the length of the threaded portion 62 of the Figure 5 spark plug.

Despite these differences in external dimensions of the spark plug body so that the spark plug of Figure 5 can be used in an outboard engine cylinder having thicker walls and a larger spark plug port, it is interesting to note that the internal dimensions and proportions as well as structure type are exactly the same in both spark plugs. Thus the cores 7 have their central electrodes "/9 located precisely the same distance from the mouth 63 of the antechamber 61 in each case. The grounded electrode 64 is mounted on exactly the same type and size of bushing 65 in the two instances and the inner ends of these bushings engage shoulders 66 in the spark plug bodies which are spaced equal distances from the antechamber openings 63.

it will be evident, therefore, that the further descrip tion or the outboard motor spark plug applies equally to the spark plugs of Figures 4 and 5. Thus the outer end of the bushing 65 has a flange 67 which fits loosely Within the cavity of the spark plug body to center the outer end of the bushing approximately as in the construction of F' c 3. The core 7 has a portion tapered toward its inner end complemental to the outwardly tapered cross section of the copper ring 71. This ring is separated from the outer end of bushing 65 by a gasket ring 72 to prevent conduction of heat from the bushing to the ring while enabling the ring to exert considerable force against the bushing axially of the spark plug to press such bushing against its seat on spark plug body shoulder 66. The core 7 in turn is held in place by the ring 73 being pressed firmly against the copper ring 74 and held in such position by the outer end 68 of the spark plug bod being bent over into overlapping relationship with it.

Preferably the end of bushing 65 engaging the spark plug body shoulder es has a flange 69 leaving a peripheral groove between such flange and flange 67 at the outer end of the bushing. The bushing is therefore spaced from t the spark plug body over most or" its axial extent, thus leaving little surface of the bushing in contact with the spark plug body. As explained in connection with the automobile spark plug of Figure 3, therefore, the transfer of heat from the bushing to the spark plug body will be deterred, whereas the transfer of heat from the core 7 to the copper ring 71 to the spark plug body may occur readily. In this type of spark plug also, therefore, the net result will be that the temperature of bushing 65 will be higher than it would be otherwise, and the temperature of the central electrode 70 will be lower. This spark plug has particularly good antifouling characteristics because of the exceptional length of the space between the electrodes and the region of contact of the core 7 with its supporting ring 71. This space includes both aportion transversely or generally radially of the spark plug axis as in the aircraft spark plug of Figure 2, and in addition an annular space extending axially of the spark plug generally like the space in the spark plugs of Figures 1 and 3. With a spark plug having a construction of this type the outboard engine can be operated at high speed, or at low'speed, or in any combination of speeds for many hours without appreciable loss of eificlency.

While the description so far has been directed to spark plugs of the antechamber type as shown in Figures 1 to 5, inclusive, the same general construction of core and grounded electrode supporting structure can be utilized in the more conventional type of spark plug without an antechamber. Thus in Figure 6 a spark plug suitable for use in an automobile engine and generally comparable to the spark plug shown in Figure 3, but without the antechamber, is shown. The internal construction of the core 5 may be generally similar to that shown in Figure 1, or even of entirely conventional type, and this core will be secured in the spark plug body as in the assembly of Figure 3.

The spark plug body 4 in the spark plug of Figure 6 is, of course, shorter than that shown in Figure 3, and in this instance the shoulder 40 at the outer end of the externally threaded portion 41 is disposed closer to the core. To allow sufficient stock in the body for cutting the threads 41 the copper ring 51 interposed between the core 5 and the body moy be of stepped external shape, but when the core is assembled in the body this ring will be forced into intimate contact both with the core and body to effect a good heat conducting structure between the core and the body.

The bushing or thirnble 43 carrying the grounded electrode 42 seats against a shoulder 44 formed in the cavity of body 40, and in order to make this bushing somewhat thinner it is preferred that a flange or rib 47 be formed on the inner end of such bushing in addition to the flange or rib 46 on the opposite end of the bushing. As in the construction of the spark plug shown in Figure 3, the copper ring 51 and the bushing 43' are separated by a heat insulating gasket 52.

The effect of the bushing 43' in poor heat transfer relationship to the body 4' in a spark plug of the type shown in Figure 6 without an antechamber will be like that in the other spark plugs described in that because of such poor heat transfer relationship heat cannot be dissipated to the engine through the spark plug body from the cavity of the spark plug mechanism as rapidly as it would be otherwise, so that the temperature of the inner periphery of bushing 43' will be higher than the temperature of a corresponding surface integral with the body would be. Further, because of such poor conductivity from the bushing 43' to the body, the portion of the spark plug body adjacent to such bushing would be lower than it would be otherwise, enabling heat to be transferred more readily from the inner tip of the core 5 to the threaded portion of the spark plug body for dissipation to the engine. The electrode 50 and core tip will consequently be at a lower temperature than they would otherwise be, with the result that the core tip and center electrode are less likely to became heated sufficiently to cause preignition. Also, because the inner wall of the spark plug mechanism cavity is hotter than usual, there will be less tendency for the spark plug to become fouled by deposit of carbon and lead compounds in the spark plug cavity.

In all of the spark plugs described the design of the cavity back of the shoulder at the larger end of the antechamber is very important to minimize fouling, and this is particularly true in the outboard engine type of spark plug shown in Figures 4 and 5, because it is customary to mix oil for lubricating purposes with the gasoline. For that reason it has the longest cavity, as well as such cavity being of considerable Width. It has been found, however, that when the central and grounded electrodes are positioned to locate the spark gap behind the shoulder at the larger portion of the antechamber as disclosed in Wright application Serial No. 163,155, lean mixtures cannot be fired effectively and considerable loss of power occurs. When the spark gap is thus located, therefore, the cavity between the tip portion of the ceramic core and the encircling wall must be designed more or less as a compromise to obtain as little fouling as possible while maintaining reasonably good power characteristics where a lean fuel mixture is being used.

In the antechamber type spark plugs disclosed above it has been found that the shape and size of the cavity behind the antechamber shoulder does not affect the ability of the spark plug to fire lean mixtures effectively if the electrodes are positioned to locate the spark gap in the antechamber itself instead of in the cavity behind the antechamber shoulder. By thus locating the electrodes,

Cir

therefore, the shape of the cavity behind the antechamher shoulder may be designed to obtain the best antifouling characteristics. The central and grounded electrodes, on the other hand, may be located in the antechamber to obtain the highest power output from the combustion of lean mixtures.

To obtain maximum power from an engine utilizing an antechamber type spark plug generally like those described above, the electrodes should be placed to locate the spark gap substantially in the maximum cross section of the antechamber, and certainly between the shoulder and a point midway between such shoulder and the neck or restricted portion of the antechamber opening through the inner end of the spark plug. If the electrodes are placed to locate the spark gap any closer to the inner end of the spark plug, it seems that the mixture nearer the opening is ignited first and tends to choke effective transmission through the antechamber opening of the burning mixture from the portion of the antechamber at the side of the spark gap remote from the antechamber opening.

Not only must the electrodes of the spark plug be kept back from the restricted opening of the antechamber through the inner end of the spark plug sufficiently far to prevent a blocking action when the gas is ignited, but the opening from the antechamber must be short enough so as not to produce any appreciable resistance to projection of the burning gas from the antechamber into the combustion space of an engine cylinder. In Figures 1 and 2 the distance between the spark gap and the neck or minimum cross-sectional portion of the opening from the antechamber is approximately seventy percent of the distance between the spark gap and the inner end of the spark plug, and preferably the portion of the distance between the spark plug and such minimum area section should not be appreciably less than that, and certainly not less than sixty percent of such distance, although such distance may be a greater proportion of the distance between the spark gap and the inner end of the spark plug as illustrated in the outboard engine spark plugs shown in Figures 4 and 5.

With the electrodes placed to locate the spark gap close to but at the antechamber side of the antechamber shoulder, the lean mixture power rating of an engine is higher than when a standard spark plug is used. The shape of the antechamber between the shoulder and its opening through the inner end of the spark plug can be designed to afford maximum power under all fuel mixture and engine speed conditions without regard to antifouling considerations. Moreover, when the end of the grounded electrode is located in overlapping relationship with the end of the central electrode, its position can be adjusted by a tool inserted through the antechamber opening to vary the width of spark gap.

We claim as our invention:

1. Spark plug mechanism comprising a hollow metal body, an insulating core having an end received in said body and including a tip portion spaced radially inward from said body, a central electrode carried by said insulating core tip portion, a bushing received in said body between said insulating core tip and said body, the exterior wall of said bushing being recessed and defining a body engaging surface alongside such recess to deter transfer of heat from said bushing to said body, and the inner end of said bushing being in sealing engagement with the inner wall of said hollow body for preventing entrance of gas into such exterior bushing wall recess, and a grounded electrode carried by said bushing and disposgd in cooperative relationship with said central electro e.

2. The spark plug mechanism defined in claim 1, in which the exterior wall of the bushing has a flange at one end thereof alongside the recess constituting the bodyengaging surface.

3. The spark plug mechanism defined in claim 2, in which the bushing has a peripheral flange at each end thereof, and the recess is located therebetween in the form of a groove.

4. Spark plug mechanism comprising a hollow metal body, an insulating core having an end received in said body and including a tip portion spaced radially inward from said body, a central electrode carried by said insulating core tip portion, a bushing received in said body between said insulating core tip and said body, the exterior wall of said bushing being recessed and defining a body engaging surface alongside such recess constituting a minor portion of the total external periphery area of said bushing to deter transfer of heat from said bushing to said body, and the inner end of said bushing being in sealing engagement with the inner wall of said hollow body for preventing entrance of gas into such exterior bushing wall recess, and a grounded electrode carried by said bushing and disposed in cooperative relationship with said central electrode.

5. The spark plug mechanism defined in claim 4, in which the bushing exterior wall has an annular groove and ribs at each side thereof defining the bushing recess and body-engaging surface.

6. The spark plug mechanism defined in claim 5, in which the exterior wall of the bushing has a plurality of annular grooves.

7. Sparks plug mechanism comprising a hollow metal body having in the hollow thereof an internal shoulder facing away from the inner end of the spark plug, a bush ing received in said body and engaging said shoulder, a ring of malleable heat conductive metal received in said body and engaging said bushing, a ceramic material core having an end portion received in said body and wedgingly engaged with said ring, means operable to hold said core pressed firmly against said ring and holding said ring pressed firmly against said bushing, a central electrode carried by said core, and a second electrode cooperating with said central electrode and grounded to said body.

8. The spark plug mechanism defined in claim 7, in which an exterior portion of the bushing received within the body hollow is recessed to space such recessed portion of the bushing exterior from the interior of the body, and the bushing exterior has a body engaging surface alongside such recess.

9. The spark plug mechanism defined in claim 7, in which the body has a second internal shoulder facing away from the inner end of the spark plug, on which the ring of malleable heat conductive metal seats.

10. A spark plug comprising a hollow metal body defining in the inner end thereof an antechamber opening through the inner end of said body and converging toward the inner body end, a shoulder within said body facing away from its inner end, a bushing received in said body, seating on said shoulder and the inner end thereof defining an inwardly projecting shoulder in said antechamber spaced from and facing toward the inner end of said body, the exterior wall of said bushing being recessed and defining a body engaging surface alongside such recess to deter transfer of heat from said bushing to said body, a ring of malleable, heat conducting metal received in said body behind said bushing, the inner periphery thereof being flared away from the inner end of said body, a ceramic material core having an inner end portion received in said body tapered inwardly complemental to and engaged with the flared periphery of said ring, means operable to hold said core pressed firmly against said ring and holding said ring pressed firmly against said body and said bushing, a central electrode carried by said core, the tip thereof projecting beyond said shoulder formed by the end of said bushing, and a grounded electrode carried by said bushing and disposed in cooperative relationship with said central electrode to define a spark gap between said bushing end shoulder and the inner end of said body.

11. The spark plug defined in claim 10, in which the spark gap is located substantially in registry perpendicular to the spark plug axis with the maximum cross-sectional area of the antechamber.

12. The spark plug defined in claim 10, in which the electrodes are placed to locate the spark gap between the bushing end formed shoulder and a point midway between such shoulder and the inner end of the spark plug body.

13. Spark plug mechanism comprising a hollow metal body having an internal shoulder facing away from its inner end, an insulating core having an end received in said body and including a tip portion spaced radially inward from said body, a central electrode carried by said insulating core tip portion, a bushing received in said body between said insulating core tip and said body, the exterior wall of said bushing being recessed and defining a body engaging surface alongside such recess to deter transfer of heat from said bushing to said body, and the inner end of said bushing being in sealing engagement with said internal shoulder of said hollow body, for preventing entrance of gas into such exterior bushing wall recess, and a grounded electrode carried by said bushing and disposed in cooperative relationship with said central electrode.

References Cited in the file of this patent UNITED STATES PATENTS 1,126,975 Furber Feb. 2, 1915 1,343,052 Heath June 8, 1920 1,359,591 Grimes Nov. 23, 1920 1,552,352 Shepherd Sept. 1, 1925 1,835,574 Rabezzana Dec. 8, 1931 1,927,500 Paulson Sept. 19, 1933 2,026,822 Close Jan. 7, 1936 2,358,911 Devine Sept. 26, 1944 2,367,840 Peters et a1. Ian. 23, 1945 2,449,403 McDougal Sept. 14, 1948 

